1. Field of the Invention
The present invention relates to an information storage medium with a structure for multi-angle data and recording and reproducing apparatuses therefor.
2. Description of the Related Art
A digital versatile disc (DVD) is a representative example of conventional information storage media on which multi-angle data can be recorded. The multi-angle data is recorded on a DVD using an interleaving method in which data is divided into units and the units are alternately recorded.
Hereinafter, a video data structure of a DVD, which is a conventional multimedia storage medium, will be described with accompanying drawings.
FIG. 1 illustrates a data structure of a DVD. Referring to FIG. 1, a DVD is divided into a video manager (VMG) area and a plurality of video title set (VTS) areas. Information regarding video title(s) and menu information for video titles are stored in the VMG area, and video title data is stored in the plurality of VTS areas. In general, the VMG area includes two or three files and each VTS area includes from three to twelve files.
FIG. 2 illustrates the data structure of a VMG area. Referring to FIG. 2, the VMG area includes a video manager information (VMGI) area containing additional information regarding the VMG area, a video object set (VOBS) area containing video object information regarding title menu, and a VMGI backup area. Each of the VMGI area, the VOBS area, and the VMGI backup area exists as a file. However, the inclusion of the VOBS area in the VMG area is optional. In some cases, the VOBS area may not be formed in the VMG area.
Each VTS area contains title information, which is a unit of reproduction, and video object information VOBS. A plurality of titles may be recorded on a VTS area.
FIG. 3 illustrates a data structure of a VTS area. Referring to FIG. 3, video title set information (VTSI), VOBS for a menu screen, VOBS for a video title set, and VTSI backup data are recorded in the VTS area. Recording of a VOBS is optional for displaying a menu screen. Each VOBS is divided into a plurality of video objects VOBs and cells which are units of record. A VOB includes of a plurality of cells. The most basic unit of record in the present invention is a cell.
In a DVD, units of reproduction are recorded in a hierarchical structure. A title is formed on the uppermost layer of the hierarchical structure. In general, a title is linked to at least one program chain (PGC). The PGC first reproduced, which is one of a plurality of PGCs, is called an entry PGC. FIG. 4 illustrates a title linked to a PGC, i.e., an entry PGC. FIG. 5 illustrates a title linked to a plurality of PGCs. When one of the plurality of PGCs is selected and reproduced after reproduction of a PGC as shown in FIG. 5, the command for determining the PGC to be selected and reproduced may be stored in a DVD. Controlling the sequence of reproduction is navigation. A command for determining navigation is contained in the program chain information (PGCI).
FIG. 6 illustrates a data structure of a PGC. Referring to FIG. 6, the PGC is stored in PGCI which is an information structure. The PGCI contains a pre-command that includes a navigation command, a post-command, and a plurality of program information. The pre-command is executed before reproduction of a PGC and the post-command is executed after reproduction. Each program contains a plurality of cell information. Cells included in a program are linked to respective cells included in a VOB which is a unit of record. Each cell, i.e., a unit of reproduction, has a cell command that is provided after reproduction thereof. The PGCI is a hierarchical description of the PGC, i.e., the unit of reproduction, and has an information structure that links a cell, which is the most basic unit of reproduction, to a cell which is the most basic unit of record.
In particular, the PGC is a link of a plurality of cells which are units of reproduction. Here, the plurality of cells may form an angle block.
FIG. 7 illustrates the structure of an angle block. Referring to FIG. 7, the angle block is constructed such that a plurality of cells are arranged in parallel so that only one of these cells can be reproduced. The cells that form the angle block, have the same reproduction time. Each of the cells corresponds to a specific angle. If the cells, which are units of reproduction, form an angle block, data for a specific angle is divided into interleaved units (ILVUs) and recorded on VOBs, which are units of record, and cells, which are units of record, using the interleaving method.
FIG. 8 illustrates the structure of a VOB and cells that are units of record when multi-angle support is not applied. Referring to FIG. 8, VOBs are sequentially stored and recorded in contiguous blocks of an information storage medium, the contiguous block being a contiguous recording space. However, as shown in FIG. 9, when multi-angle support is applied, VOBs for each angle and their cells are recorded in ILVUs on an interleaved block, using the interleaving method. As a result, data for a specific angle is not recorded on contiguous record areas. That is, angle data is sequentially, alternatively recorded using the interleaving method.
FIG. 9 illustrates angle data of two that is sequentially and alternately recorded using the interleaving method. Referring to FIG. 9, respective ILVUs have the same reproduction time. The amount of data to be recorded may vary according to the type of a compression method used. In the case of interleaved data, in order to reproduce data for an angle or reproduce data for a changed angle, a jump must be made to desired ILVUs. For instance, in order to reproduce data in a first angle, the data for the first angle in the ILVU must be detected. For this end, a video object bit stream contains data NXT ILVU_SA and NXT ILVU_SZ in the structure shown in FIG. 11, that indicate the position and size of the next ILVU data belonging to a bit stream. After reproduction of the ILVU data, a jump to the next ILVU data is made using the data NXT ILVU_SA and NXT ILVU_SZ. In order to change angles during the data reproduction, a jump must be made to the position of data for the changed angle. The extent of jumping is determined in ILVUs.
FIG. 10 illustrates jumping to data for a selected angle in view of cells. Referring to FIG. 10, even if a user issues a command to change angles at a certain time during reproduction of ILVU data, the subsequent image data can be reproduced without pause for a seamless change. This is accomplished by first completing the reproduction of ILVU data, following a link by jumping to ILVU data for the changed angle, and reproducing the ILVU data for the changed angle. Information regarding the position of ILVU data is multiplexed and contained in a bit stream of video object data that is recorded using the interleaving method.
FIG. 12 illustrates the structure of information SML_AGL_Cn_DSTA contained in a video object bit stream specifying the positions and sizes of ILVU data for nine angles (n is a natural number between 1 and 9). The maximum number of angles supported by a DVD is nine. The data SML_AGL_Cn_DSTA provides information regarding the ILVU data for angle #n through a link in the current ILVU data. After the reproduction of the current ILVU data, it is possible to change a current angle to a desired angle and reproduce data for the desired angle, using the data SML_AGL_Cn_DSTA.
In a DVD authoring process for multi-angle data support, images photographed at different angles are compressed to form several bit streams of data with the same reproduction length. Next, a bit stream is formed using the interleaving method and information is inserted into each bit stream, which allows a reference to other angles during data reproduction. Accordingly, video object data is recorded on a DVD such that angles can be changed during data reproduction.
However, if multi-angle data is divided into units and stored in a DVD using the interleaving method, the multi-angle data is not continuously recorded in contiguous areas of the DVD. Thus, for continuous reproduction of data for an angle, a reproducing apparatus is required to move its position many times to read the data. In particular, if a reproducing apparatus reproduces data from an optical disc or a hard disc, considerable time is spent by the apparatus to change its position. There is also a bit rate limit imposed on a compressed bit stream to compensate for the time delay offset caused when the apparatus changes its position.